1. Field of the Invention
The present invention relates to a method and apparatus for manufacturing a color filter by forming and arranging a large number of colored filter elements on a transparent substrate, the color filter, a display apparatus, an apparatus having the display apparatus, and a method of equalizing the colored states of areas.
2. Description of the Related Art
With recent advances in personal computers, especially portable personal computers, the demand tends to arise for liquid crystal displays, especially color liquid crystal displays. However, in order to further popularize the use of liquid crystal displays, a reduction in cost must be achieved. Especially, it is required to reduce the cost of a color filter which occupies a large proportion of the total cost. Various methods have been tried to satisfy the required characteristics of color filters while meeting the above requirements. However, any method capable of satisfying all the requirements has not been established. The respective methods will be described below.
The first method is a dyeing method, which is the most popular method. In the dyeing method, a water-soluble polymer material as a dyeable material is coated on a glass substrate, and the coating is patterned into a desired shape by a photolithography process. The obtained pattern is dipped in a dye bath to obtain a colored pattern. This process is repeated three times to form R, G, and B color filter layers.
The second method is a pigment dispersion method, which is currently replacing the dyeing method. In this method, a pigment-dispersed photosensitive resin layer is formed on a substrate and patterned into a single-color pattern. This process is repeated three times to obtain R, G, and B color filter layers.
The third method is an electrodeposition method. In this method, a transparent electrode is patterned on a substrate, and the resultant structure is dipped in an electrodeposition coating fluid containing a pigment, a resin, an electrolyte, and the like to be colored in the first color by electrodeposition. This process is repeated three times to form R, G, and B color filter layers. Finally, these layers are calcined.
The fourth method is a print method. In this method, a pigment is dispersed in a thermosetting resin, a print operation is performed three times to form R, G, and B coatings separately, and the resins are thermoset, thereby forming colored layers. In either of the above methods, a protective layer is generally formed on the colored layers.
The point common to these methods is that the same process must be repeated three times to obtain layers colored in three colors, i.e., R, G, and B. This causes an increase in cost. In addition, as the number of processes increases, the yield decreases. In the electrodeposition method, limitations are imposed on pattern shapes which can be formed. For this reason, with the existing techniques, this method cannot be applied to TFTs. In the print method, a pattern with a fine pitch cannot be formed because of poor resolution and poor evenness.
In order to eliminate these drawbacks, methods of manufacturing color filters by an ink-jet system are disclosed in Japanese Patent Laid-Open Nos. 59-75205, 63-235901, and 1-217320. In these methods, coloring solutions containing coloring agents of three colors, i.e., R (red), G (green), and B (blue), are sprayed on a transparent substrate by an ink-jet system, and the respective coloring solutions are dried to form colored image portions. In such an ink-jet system, R, G, and B filter elements (pixels) can be formed at once, allowing great simplification of the manufacturing process and a great reduction in cost.
In the above conventional manufacturing methods based on the ink-jet system, however, it is difficult to discharge a required amount of ink for one filter element (one pixel) at once and uniformly spread the ink on the entire surface of each opening portion of a black matrix for partitioning off each filter element. In addition, each discharged ink dot has an almost circular shape, and a plurality of ink dots must be discharged onto each rectangular opening portion of the black matrix. In this case, it is difficult to uniformly spread the ink on the entire surface of each opening portion of the black matrix by using a method of uniformly discharging an ink. Color omissions occur sometimes at peripheral portions of an opening portion. A color omission is a serious defect for a color filter, and causes a great deterioration in image quality. If a considerably larger dot is formed on an opening portion of a black matrix in order to prevent such an inconvenience, the dot may mix with a dot of another color in an adjacent opening portion. In order to solve this problem, various proposals associated an improvement in the properties of inks and reception layers have been made.
The experiment conducted by the present applicant shows that the behavior of inks after impact greatly varies depending on the characteristics of red (R), green (G), and blue (B) inks and the like. That is, only with an improvement in the properties of inks and reception layers, it is difficult to manufacture a color filter without color irregularity by using an ink-jet system. As described above, an ink discharging method and discharging amount are important factors in manufacturing a color filter.